Does “Alpine Pumping” have an effect on the ventilation of Munich?

Alpine Pumping refers to a thermally driven circulation between the Alps and the Alpine foreland in southeastern Germany, which occurs regularly under clear and calm weather conditions (e.g. Lugauer and Winkler (2005)). Earlier studies suggest, that the ventilation of the city of Munich, and thus the urban temperature distribution, could be influenced by this regional wind system.

The present work was conducted in a cooperation framework between the city of Munich and the German Meteorological Service. The occurrence of Alpine Pumping and its effect on the temperature distribution in the city of Munich were investigated by temporary and operational wind measurements as well as numerical simulations. The thermal wind system was simulated with the regional climate model COSMO-CLM and the characteristics of Alpine Pumping deduced from this simulation used as input for the high-resolution urban climate model MUKLIMO_3.

Using a radiation-based criterion, Alpine Pumping occurs on about 60 days per year, mostly in the summer months when the heat load is highest. The wind fields of temporary measurements in the rural areas south of Munich show the expected daily cycle of the wind system, especially the southerly flow during the night, which transports cold air from the mountains into the city. An influence of the regional circulation pattern on the temperature in the city area was found in a case study with the urban climate model MUKLIMO_3. Especially at night and in the morning hours, the cooler air from the surroundings ventilates the city area. Furthermore, the model results show a spatial shift of the maximum heat island in Munich during the course of the day.

The findings show, that Alpine Pumping is a rather frequent phenomenon in the study area and represents an important contribution to the natural ventilation of different areas within the city.

 

References:

LUGAUER, M., WINKLER, P., 2005: Thermal circulation in South Bavaria - climatology and synoptic aspects. Meteorologische Zeitschrift. 14, 15-13.